| Emission materials are related to the device efficiency,stability and fabrication cost of Organic light-emitting Diodes(OLED),which are the core issues in this research field.The development of low-cost and high-performance emission materials will further expand the application range of OLED.The new spiral cyclic aromatic Spiro [fluorene-9,9?-xanthene](SFX)has the advantages of one-pot synthesis and good stability.At the same time,its dualized aromatic structure provides a widespace for structure derivation and molecular design.In this paper,D-A-D fluorescence molecules 2-SFX-BT and 2?-SFX-BT based on SFX and benzothiazole(BT)were successfully prepared by Miyaura borylation and Suzuki coupling reaction.The structure of the product was characterized by 1H NMR spectrum,maldi-tof mass spectrum and X-ray single crystal diffractometer.The photophysical properties of the two compounds were tested by UV-visible absorption spectra and steady/transient fluorescence emission spectra.In the dilute chloroform solution,the maximum absorption wavelength of both compounds was about 409 nm and the emission peak was around 529 nm.The analysis of discoloration effect of solvent shows that the fluorescence emission of the two compounds originated from the charge transfer excited state between the SFX and the BT units within the molecule.The HOMO/LUMO energy levels of 2-SFX-BT and 2?-SFX-BT were measured by cyclic volt-ampere analysis,and the HOMO/LUMO energy levels of 2-SFX-BT and 2?-SFX-BT were-5.78 e V/-2.92 e V and-5.65 e V/-2.99 e V,respectively.Using 2-SFX-BT and 2?-SFX-BT as fluorescent emission materials and Bis[2-(diphenylphosphino)phenyl] ether oxide(DPEPO)as main material,the doped devices were prepared by vacuum evaporation.Under the doping concentration of 30 wt%,the maximum current efficiency(CE)of 2-SFX-BT and 2?-SFX-BT devices was 15.67 cd/A and 16.24 cd/A,respectively.The maximum power efficiency(PE)is 15.38 lm/W and 15 lm/W,respectively.The highest external quantum efficiency(EQE)was 4.76% and 5.02%,respectively.The maximum brightness of the device can reach 17600 cd/m~2 and 17990 cd/m~2 respectively.In view of the resistance to concentration quenching of SFX steric resistance structure,the electroluminescence properties of two material undoped devices were further investigated.The emission peaks of the undoped devices are all located at 525 nm,and no drift or broadening occurs in the electrogenerated spectra under 4 ? 10 V operating voltages,indicating that the carriers are fully compounded in the emission layer.The maximum CE of 2-SFX-BT and 2?-SFX-BT undoped devices was 13.75 cd/A and 14.02 cd/A,PE was 7.71 1m/W and 8.81 1m/W,and EQE was 4.08% and 4.25%,respectively.Based on the analysis of photophysical properties,crystal stacking structure and electroluminescence performance,it can be concluded that the construction of D-A-D fluorescent material by using the 2?-position of SFX is beneficial to enhance the radiation transition of charge transfer state and weaken the intermolecular aggregation,so as to obtain high-performance fluorescent material.The results provide experimental basis and new molecular design ideas for the development of OLED emission materials based on SFX. |
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